FBI Director James Comey responded, May 3, before the Senate Judiciary Committee to a question from Sen. Dianne Feinstein (D-Calif.) on his announcement about re-opening the probe into Hillary Clinton's use of a private email server days before the election. (Reuters)

They were whispering it on election night, and almost six months later Democrats are basically shouting it: FBI Director James B. Comey cost them the presidential election by telling Congress 11 days before the vote that the agency was reading newly discovered Hillary Clinton emails.

Here's Clinton herself in an interview with CNN's Christiane Amanpour on Tuesday: “I was on the way to winning until the combination of Jim Comey's letter on October 28 and Russian WikiLeaks raised doubts in the minds of people who were inclined to vote for me but got scared off.”

And here's Sen. Dianne Feinstein (Calif.), the top-ranking Democrat on the Senate Judiciary Committee, on Wednesday: “I join those who believe the action taken by the FBI did, in fact, have an impact on the election.”

Comey has repeatedly defended his decision, saying that to conceal new information about an FBI investigation from Congress — especially when Congress thought the investigation was complete — would be worse than any potential political consequences of saying something less than two weeks before the election. But if Comey has ever had any frustration about Democrats doubting him, he has kept it to himself. Until now.

When Feinstein pressed the FBI chief Wednesday at a Senate Judiciary Committee hearing to explain why Comey told Congress about emails found on the computer of the ex-husband of then-Clinton aide Huma Abedin, Comey did something rare for Comey: He got emotional.

Here's part of his answer (see video above for expanded version):

Look, this is terrible. It makes me mildly nauseous that we have to have some impact on the election. But honestly it wouldn't change the decision.

Everybody who disagrees with this has to come back to Oct. 28 with me and stare at this and tell me what you would do. Would you speak, or would you conceal?

And I could be wrong, but we honestly made a decision between those two choices that, even in hindsight, and this has been one of the world's most painful decisions, I would make the same decision. I would not conceal that from the Congress. … And reasonable people can disagree, but that's the reason I made the choice, and it was a hard choice, but I still believe in retrospect it was the right choice.

When Feinstein asked Comey if there was anyone on his staff who felt differently, the FBI chief said, “No.”

“It was a great debate,” Comey said. “And one of my junior lawyers said, 'Should you consider that what you're about to do may help elect Donald Trump president?' And I said: 'Thank you for raising that.' Not for a moment, because down that path lies the death of the FBI as an independent institution in America. I can't consider for a second whose political fortunes will be affected in that way.”

Feinstein was not persuaded. “I look at this exactly the opposite way you do,” she said. "Everybody knew that it would influence the [election] ... that there was a very large percentage of chance that it would, and yet that percentage of chance was taken, and there was no information, and the election was lost.”

In the same way we probably won't know how much the Russian meddling to help elect Donald Trump actually helped Trump, we will probably never know how much the FBI's decision to raise new questions about Clinton's emails just before the election influenced the election.

There's evidence for both sides to make their point. An October Washington Post-ABC News poll conducted just before the election found that a majority of likely voters said they were unmoved by the FBI's announcement on Clinton's emails. But 34 percent of likely voters did say the FBI's review makes them less likely to support Clinton.

Still, we don't know whether those voters were going to vote for Clinton in the first place. Clinton certainly thinks so.

Comey, we should emphasize, is not arguing one way or the other about whether his announcement influenced the election. He's just arguing that telling Congress about Clinton's emails was the best of two bad options. But he and Democrats are still at loggerheads about whether he should have said anything at all. It doesn't look like they'll reach a mutual understanding anytime soon.

Emily Guskin contributed to this report.